Effect of anionic salts on rumen fermentation in a continuous culture system

Abstract Text: The objective was to determine if anionic salt products (AS), commonly used to lower dietary cation-anion difference (DCAD) in pre-fresh dairy cattle diets, altered ruminal digestion, microbial fermentation, or microbial yield in a single-flow continuous culture system. Two consecutive experiments were conducted using 24 fermenters inoculated with rumen fluid from two lactating Holstein cows. For Exp. 1 fermenters were fed a basal diet twice daily (47.12 g DM/d; 37% wheat hay, 26% corn silage, 12.5% soybean meal, 11% soy hulls, 13.5% supplement on a DM basis). Treatments (0.19 g/d) were added directly to randomly assigned fermenters (4 per treatment) and consisted of control (CON; basal diet only), soybean meal (SBM), urea (URE), chloride and sulfur containing AS blend (CSB), glutamic acid fermentation product (GAF), and hydrochloric acid based product (HCB). In Exp. 2 the same basal diet was used except CSB and GAF treatments were blended to the basal diet at 0.077 and 0.146 g/d, respectively, and other treatments blended to achieve 0.19 g/d (representing approximate adjustments for equivalent DCAD content from respective AS). Diets were fed for 7 d with 4 d adaptation and 3 d sampling. Passage rate was 5.47% for Exp. 1 and 4.83% for Exp. 2. Fermenter samples for VFA and ammonia analysis were collected at 0 and 4h after morning feeding. Outflow was collected daily and fermenter content collected at the end of the experiment. Data were analyzed as a completely randomized design with fermenters as experimental unit, using the MIXED procedure of SAS (Version 9.3, Cary, NC). In Exp. 1 NDF digestibility (%) tended to be lower (P = 0.088) for GAF (31.9) and HCB (33.0) compared to other treatments except SBM (37.4). Ammonia concentration (mg NH₃ N/dL) for URE was greater (22.2; P < 0.01) than other treatments, with CSB greater (19.5; P < 0.04) than SBM (18.3) and CON (18.5). These differences were not found in Exp. 2. In both experiments, there were no effects on OM, CP, or ADF digestibility, microbial efficiency, microbial flow, or VFA. Differences in NDF digestibility and ammonia concentration between Exp. 1 and Exp. 2 may be due to run to run variability. In conclusion, adding anionic salt products to a pre-fresh dairy cattle diet had no detrimental effects on ruminal digestibility or microbial fermentation and yield.

Keywords: anionic salts, rumen fermentation, continuous culture